fix(core): shadow-aware incremental damage bounds

[RtlZeroMemory]

Summary

• fix incremental redraw culling to use shadow-aware bounds for box widgets
• include shadow extents when building per-instance and per-id damage rect indexes
• preserve previous-frame shadow-aware bounds so removals/toggles clean up correctly
• add regression coverage ensuring partial redraw matches full frame when updates hit shadow-only overlap regions

Root Cause

Incremental redraw used layout rects (box body only) for damage intersection and child culling. Box shadows are rendered outside those rects (right/bottom), so shadow-only intersections were skipped and stale artifacts could remain until a full redraw/resize.

Validation

• npm run lint
• npm run typecheck
• npm run build
• npm run test

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 7144acb8c4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Recompute shadow damage bounds on layout-skipped commits

appendDamageRectForInstanceId now pulls from _pooledDamageRectByInstanceId, but that map is only rebuilt during the layout-index pass (buildLayoutRectIndexes), so commits that skip layout can use stale shadow-aware bounds. Because shadow changes are not layout-driving, toggling a box shadow on (or increasing offsets) in a commit with layout: false can produce an undersized damage region, so incremental redraw clips away part of the newly visible shadow until a later full/layout render.

Useful? React with 👍 / 👎.